Arsenite transport into paddy rice (Oryza saliva) roots.

Here the mechanism of arsenite transport into paddy rice (Oryza sativa) roots, uptake of which is described by Michaelis-Menten kinetics, is reported. A recent study on yeast (Saccharomyces cerevisiae) showed that undissociated arsenite (its pK(a) is 9.2) was transported across the plasma membrane via a glycerol transporting channel. To investigate whether the same mechanism of transport was involved for rice, competitive studies with glycerol, which is transported into cells via aquaporins, were performed.

Glycerol competed with arsenite for transport in a dose-dependent manner, indicating that arsenite and glycerol uptake mechanisms were the same. Arsenate transport was unaffected by glycerol, confirming that arsenate and arsenite are taken up into cells by different mechanisms.

Antimonite, an arsenite analogue that is transported into S. cerevisiae cells by aquaporins, also competed with arsenite transport in a dose-dependent manner, providing further evidence that arsenite is transported into rice roots via glycerol transporting channels. Mercury (Hg2+) inhibited both arsenite and arsenate uptake, suggesting that inhibition of influx was due to general cellular stress rather than the specific action of Hg2+ on aquaporins.

Arsenite uptake by pea (Pisum sativum) and wheat ( Triticum aestivum) was also described by Michaelis-Menten kinetics.